Permeable polyaniline articles for gas separation

Abstract

Immersion precipitation of solutions having 15%-30% (w/w) and various molecular weights of the emeraldine base form of polyaniline in polar aprotic solvents are shown to form integrally skinned asymmetric membranes and fibers having skin layers <1 μm thick which exhibit improved rates of gas transport while preserving good selectivity. These membranes can be further transformed by an acid doping process after fabrication to achieve excellent permeation rates and high selectivities for particular gas separations. Prior to the use of concentrated EB solutions, the formation of integrally skinned asymmetric membranes was not possible, since films and fibers made from <5% w/w polyaniline solutions were found to disintegrate during the IP process.

What is claimed is:  
     
       1. A method for preparing a gas-selective, permeable integrally skinned asymmetric membrane (ISAM) which comprises the steps of: 
       (a) forming a solution including the emeraldine base form of polyaniline having between 15% and 30% by weight of polyaniline;  
       (b) pouring the solution onto a substrate forming thereby a membrane; and,  
       (c) immersing the membrane in a nonsolvent for polyaniline; thereby causing the emeraldine base form of polyaniline to precipitate forming an ISAM having a permeable dense skin in the vicinity of the surface of contact of the membrane with the nonsolvent and a lower density porous support portion wherein a gel inhibitor is added to the solution of the emeraldine base form of polyaniline before said step of pouring the solution.  
     
     
       2. The method as described in  claim 1 , wherein the emeraldine base form of polyaniline comprises polyaniline having M W ≧53,000. 
     
     
       3. The method as described in  claim 1 , wherein the nonsolvent for polyaniline comprises water. 
     
     
       4. The method as described in  claim 1 , wherein the gel inhibitor is selected from the group consisting of primary, secondary and tertiary amines. 
     
     
       5. The method as described in  claim 1 , further including the step of drying the membrane after said step of immersing the membrane in a nonsolvent for polyaniline. 
     
     
       6. A method for preparing a gas-selective, permeable integrally skinned asymmetric membrane (ISAM) which comprises the steps of: 
       (a) forming a solution of the emeraldine base form of polyaniline having between 15% and 30% by weight of polyaniline;  
       (b) pouring the solution onto a substrate forming thereby a membrane;  
       (c) immersing the membrane in a nonsolvent for polyaniline, thereby causing the emeraldine base form of polyaniline to precipitate forming an ISAM having a permeable dense skin in the vicinity of the surface of contact of the membrane with the nonsolvent, and a lower density porous support portion; and, caulking the dense skin after said step of immersing the membrane in a nonsolvent for polyaniline.  
     
     
       7. The method as described in  claim 6 , wherein the caulking compound comprises silicon elastomer. 
     
     
       8. The method as described in  claim 7 , wherein the silicon elastomer comprises polydimethylsiloxane. 
     
     
       9. The method as described in  claim 1 , further comprising the step of adjusting the thickness of the membrane after said step of pouring the solution onto a substrate. 
     
     
       10. The method as described in  claim 1 , further comprising the step of heating the ISAM in order to improve gas selectivity. 
     
     
       11. The method as described in  claim 1 , further comprising the step of acid doping the ISAM in order to improve gas selectivity. 
     
     
       12. A method for preparing a gas-selective, permeable integrally skinned asymmetric membrane (ISAM) which comprises the steps of: 
       (a) forming a solution including the emeraldine base form of polyaniline having between 15% and 30% by weight of polyaniline and a polymer other than polyaniline;  
       (b) pouring the solution onto a substrate forming thereby a membrane; and, (c) immersing the membrane in a nonsolvent for polyaniline, thereby causing the emeraldine base form of polyaniline to precipitate forming a blended polymer ISAM having a permeable dense skin in the vicinity of the surface of contact of the membrane with the nonsolvent, and a lower density porous support portion.  
     
     
       13. The method as described in  claim 12 , wherein said polymer other than polyaniline comprises polysulfone.